package summer.string;

public class Solution28 {
    public int strStr(String haystack, String needle) {
        int[] next = getNext(needle);
        int j = 0;
        for (int i = 0; i < haystack.length(); i++) {
            while (j > 0 && haystack.charAt(i) != needle.charAt(j)) j = next[j - 1];
            if (haystack.charAt(i) == needle.charAt(j)) j++;
            if (j == needle.length()) return i - j + 1;
        }
        return -1;
    }

    public int[] getNext(String s) {
        int[] next = new int[s.length()];
        next[0] = 0;
        int j = 0;
        for (int i = 1; i < s.length(); i++) {
            while (j > 0 && s.charAt(i) != s.charAt(j)) j = next[j - 1];
            if (s.charAt(i) == s.charAt(j)) j++;
            next[i] = j;
        }
        return next;
    }
}
